B77E/L/F Fuel Flow Abnormalities

Was doing a Long Haul Session in the B77F and the fuel consumption seemed off and noticed FF was decreasing if thrust was advanced beyond 100% N1 in stable flight.

Device: iPhone13PM
Operating system:15.6

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You seem to be going quite fast for the B77F. Even though the max is Mach 0.87 – Mach 0.89, the cruise speed is Mach 0.84. Try slowing down to 0.84 for better cruise performance.


It appears that you still have 12 and a half hours to your destination which means your aircraft is full of fuel. Starting your cruise at 37.000ft is dangerous when that heavy in a 777.
I would recommend step climbing when flying Very Long Haul routes.

Then the 777 has a cruising speed of M0.84 ideally. At M0.88 you will be consuming too much fuel.

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@Chris_Wing @Mathurin_Garcier

The original poster isn’t saying anything about cruise alt or performance issues.

Look at the fuel flow in the 2 pictures provided, the fuel flow is higher in the lower thrust setting picture. Which is clearly an issue.


Well time to start testing and reporting the issue 🙃

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Hey 👋☺️ I fly the 77F frequently and I recommend to fly FL300-330 in the beginning by a speed of 0.85 . You will have fuel flow of 5800 - 6500 KG ( without headwind ) . Don’t climb to FL370 intial . It’s to high for that weight :)

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Yes true my bad

This wasn’t my first ULH nor the first in the B77F.

7h39 min into planned 21:04; started step at 29>31>33
M.86 SPD HOLD (M.85 actual) to stay above min clean speed. Wind was the reason for the climb to FL370 and was willing to accept an increase in cruise speed and the associated fuel consumption for the weight. That’s when I noticed the FF abnormally.

100% thrust should not consume LESS fuel than 73%.

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Thanks for paying attention.

Can replicate, seems like at FL370 there is a major decrease in fuel burn around 70% throttle. Above that, it steadily decreases until max throttle which doesn’t make much sense


I did a few rough tests and it seems that the change-over to Mach at FL280 throws a bug into the fuel flow algorithms.

*Edit to add:

It affects all the 777-200; ER/LR/&F variants as it seems they use the same flight dynamics in a similar manner to how the CRJ family is. A bit disappointing IMO.

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